The present invention relates generally to circuits for controlling rotation of motors, and more particularly to a circuit which controls the rotation of a motor by a type of a phase locked loop (PLL), by using a signal in which a signal responsive to the phase difference between an output velocity signal of a frequency generator which is responsive to the rotation of the motor and a reference signal, and a signal responsive to the velocity signal frequency, are multiplexed.
As an example of a conventional circuit for controlling the rotation of a motor in a record player, tape recorder, and the like, for example, there has been a circuit comprising a frequency-voltage converting circuit including a first sawtooth wave generating circuit supplied with the output of a frequency generator which is connected to a rotary shaft of a motor, and a first sample-and-hold circuit, phase difference-voltage converting circuit including a second sawtooth wave generating circuit supplied with the outputs of a reference signal generator and the above frequency generator, and a second sample-and-hold circuit, and a circuit for adding the outputs of the above frequency-voltage converting circuit and the phase difference-voltage converting circuit, to control the rotational driving of the motor by the added output thus obtained.
However, in this conventional circuit, the circuit construction became complex since a total of two sample-and-hold circuits were required for each of the above frequency-voltage converting circuit and the phase difference-voltage converting circuit, and suffered disadvantages in that the number of circuit elements became large and the circuit could not be manufactured at low cost. Especially when realizing the circuit in an integrated circuit (IC), noise due to the leak current in the sample-and-hole circuit is large, and problems are introduced upon forming of the above integrated circuit.